The annexation of Crimea - and likely annexation of more of the eastern Ukraine - and the inability of the West to do anything about it - has probably killed the Nuclear Non-Proliferation Treaty and forced a lot of countries to go nuclear.
After the dissolution of the Soviet Union, Ukraine inherited the third-largest nuclear weapons arsenal in the world. In 1992 it agreed to give up all nuclear weapons to Russia for disposal and to join the Nuclear Non-Proliferation Treaty as a non-nuclear weapon state.
Obviously the Ukraine would not give up its nuclear weapons without some security guarantee from those asking them to give up the nukes. Not with Russia next door, which had occupied them for decades and had committed genocide against them.
Now, that promise doesn't agree to protect the Ukraine from non-nuclear attacks. But it does promise that the US, Britain and Russia would "respect the Independence and Sovereignty and the existing borders of Ukraine."
(It also agrees to protect the Ukraine against the threat of aggression with nukes. And the big reason that Russia can get away with invading the Ukraine where the US or UN has stepped in after other invasions, is obviously that Russia has nukes.)
So the US and Russia and Britain jointly presented a promise to Ukraine to get them to lower their defenses. And now one of them has violated that promise. Whether or not that makes for a legal obligation on the part of the others to set things right, it certainly makes for an ethical one.
But it doesn't stop there:
All of the other non-nuclear-weapon states under the Non-Proliferation Treaty - those who have agree not to build nukes or to give up their nuclear weapons capability - are being taught a harsh lesson: Nukes are what counts. No-one will protect you when a nuclear power invades you. Not even those who jointly promised and signed Security Assurances with the invader.
It's already hard enough to convince other countries that "YOU shouldn't have nukes to protect yourself, but WE should." A big part of that convincing is "WE will protect you from threats that being a nuclear power would otherwise have prevented." And "WE act as a balance against the other nuclear power (namely Russia) attacking you."
This is where we find out whether the assurance under the Non-Proliferation Treaty are worth anything, or whether everyone should start nuclear programs.
Actually, that question seems to have been answered.